external statements will not work if interfaces exist

we're currently providing a patch for PETSc with interfaces for all
functions that we use

src/DAMASK_FEM.f90

@@ -118,11 +118,8 @@ program DAMASK_FEM
 
  external :: &
    MPI_abort, &
-   DMGetDimension, &
-   DMGetLabelSize, &
-   DMGetLabelIdIS, &
-   ISDestroy, &
    quit
+
 !--------------------------------------------------------------------------------------------------
 ! init DAMASK (all modules)
  call CPFEM_initAll(el = 1_pInt, ip = 1_pInt)

src/DAMASK_interface.f90

@@ -88,9 +88,7 @@ subroutine DAMASK_interface_init()
    dateAndTime                                                                                      ! type default integer
  PetscErrorCode :: ierr
  external :: &
-   quit,&
+   quit
-   PETScErrorF, &                                                                                   ! is called in the CHKERRQ macro
-   PETScInitialize
 
  open(6, encoding='UTF-8')                                                                          ! for special characters in output
 

src/DAMASK_spectral.f90

@@ -151,7 +151,6 @@ program DAMASK_spectral
  external :: &
    quit
 
-
 !--------------------------------------------------------------------------------------------------
 ! init DAMASK (all modules)
  call CPFEM_initAll(el = 1_pInt, ip = 1_pInt)
@@ -659,9 +658,6 @@ subroutine quit(stop_id)
  PetscErrorCode :: ierr = 0
  logical :: ErrorInQuit
  
- external :: &
-   PETScFinalize
-
  call PETScFinalize(ierr)
  if (ierr /= 0) write(6,'(a)') ' Error in PETScFinalize'
 #ifdef _OPENMP

src/FEM_mech.f90

@@ -62,7 +62,6 @@ module FEM_mech
    FEM_mech_solution ,&
    FEM_mech_forward, &
    FEM_mech_destroy
- external :: PETScerrorf
 contains
 
 !--------------------------------------------------------------------------------------------------

src/FEM_utilities.f90

@@ -121,7 +121,6 @@ use PETScis
    COMPONENT_MECH_Z_ID, &
    COMPONENT_THERMAL_T_ID
 
- external :: PETScErrorF
 contains 
 
 !--------------------------------------------------------------------------------------------------

src/numerics.f90

@@ -192,8 +192,6 @@ subroutine numerics_init
    tag ,&
    line
 !$ character(len=6) DAMASK_NumThreadsString                                                         ! environment variable DAMASK_NUM_THREADS
- external :: &
-   PETScErrorF                                                                                      ! is called in the CHKERRQ macro
 
 #ifdef PETSc
  call MPI_Comm_rank(PETSC_COMM_WORLD,worldrank,ierr);CHKERRQ(ierr)

src/spectral_damage.f90

@@ -50,8 +50,6 @@ module spectral_damage
    spectral_damage_init, &
    spectral_damage_solution, &
    spectral_damage_forward
- external :: &
-   PETScErrorF                                                                                      ! is called in the CHKERRQ macro
 
 contains
 
@@ -85,11 +83,6 @@ subroutine spectral_damage_init()
  Vec :: uBound, lBound
  PetscErrorCode :: ierr
  character(len=100) :: snes_type
- external :: &
-   SNESSetOptionsPrefix, &
-   SNESGetType, &
-   DMDAGetCorners, &
-   DMDASNESSetFunctionLocal
 
  write(6,'(/,a)') ' <<<+-  spectral_damage init  -+>>>'
  write(6,'(/,a)') ' Shanthraj et al., Handbook of Mechanics of Materials, volume in press, '
@@ -194,11 +187,6 @@ type(tSolutionState) function spectral_damage_solution(timeinc,timeinc_old,loadC
  PetscErrorCode :: ierr   
  SNESConvergedReason :: reason
 
- external :: &
-   VecMin, &
-   VecMax, &
-   SNESSolve
-
  spectral_damage_solution%converged =.false.
  
 !--------------------------------------------------------------------------------------------------

src/spectral_mech_Basic.f90

@@ -66,8 +66,6 @@ module spectral_mech_basic
    basic_init, &
    basic_solution, &
    basic_forward
- external :: &
-   PETScErrorF                                                                                      ! is called in the CHKERRQ macro
 
 contains
 
@@ -119,11 +117,6 @@ subroutine basic_init
  integer(pInt) :: proc
  character(len=1024) :: rankStr
  
- external :: &
-   SNESSetOptionsPrefix, &
-   SNESSetConvergenceTest, &
-   DMDASNESSetFunctionLocal
-   
  write(6,'(/,a)') ' <<<+-  DAMASK_spectral_solverBasic init  -+>>>'
  write(6,'(/,a)') ' Shanthraj et al., International Journal of Plasticity, 66:31–45, 2015'
  write(6,'(a,/)') ' https://doi.org/10.1016/j.ijplas.2014.02.006'
@@ -246,9 +239,6 @@ type(tSolutionState) function basic_solution(incInfoIn,timeinc,timeinc_old,stres
  PetscErrorCode :: ierr   
  SNESConvergedReason :: reason
 
- external :: &
-   SNESsolve
-
  incInfo = incInfoIn
 
 !--------------------------------------------------------------------------------------------------

src/spectral_mech_Polarisation.f90

@@ -73,8 +73,6 @@ module spectral_mech_Polarisation
    Polarisation_init, &
    Polarisation_solution, &
    Polarisation_forward
- external :: &
-   PETScErrorF                                                                                      ! is called in the CHKERRQ macro
 
 contains
 
@@ -130,11 +128,6 @@ subroutine Polarisation_init
  integer(pInt) :: proc
  character(len=1024) :: rankStr
  
- external :: &
-   SNESSetOptionsPrefix, &
-   SNESSetConvergenceTest, &
-   DMDASNESsetFunctionLocal
-   
  write(6,'(/,a)') ' <<<+-  DAMASK_spectral_solverPolarisation init  -+>>>'
  write(6,'(/,a)') ' Shanthraj et al., International Journal of Plasticity, 66:31–45, 2015'
  write(6,'(a,/)') ' https://doi.org/10.1016/j.ijplas.2014.02.006'
@@ -272,9 +265,6 @@ type(tSolutionState) function Polarisation_solution(incInfoIn,timeinc,timeinc_ol
  PetscErrorCode :: ierr   
  SNESConvergedReason :: reason
 
- external :: &
-   SNESSolve
-
  incInfo = incInfoIn
 
 !--------------------------------------------------------------------------------------------------

src/spectral_thermal.f90

@@ -50,8 +50,6 @@ module spectral_thermal
    spectral_thermal_init, &
    spectral_thermal_solution, &
    spectral_thermal_forward
- external :: &
-   PETScErrorF                                                                                      ! is called in the CHKERRQ macro
 
 contains
 
@@ -88,11 +86,6 @@ subroutine spectral_thermal_init
  PetscScalar,  dimension(:,:,:), pointer     :: x_scal
  PetscErrorCode :: ierr
 
- external :: &
-   SNESsetOptionsPrefix, &
-   DMDAgetCorners, &
-   DMDASNESsetFunctionLocal
-   
  write(6,'(/,a)') ' <<<+-  spectral_thermal init  -+>>>'
  write(6,'(/,a)') ' Shanthraj et al., Handbook of Mechanics of Materials, volume in press,'
  write(6,'(/,a)') ' chapter Spectral Solvers for Crystal Plasticity and Multi-Physics Simulations. Springer, 2018'
@@ -196,11 +189,6 @@ type(tSolutionState) function spectral_thermal_solution(timeinc,timeinc_old,load
  PetscErrorCode :: ierr   
  SNESConvergedReason :: reason
 
- external :: &
-   VecMin, &
-   VecMax, &
-   SNESSolve
-
  spectral_thermal_solution%converged =.false.
  
 !--------------------------------------------------------------------------------------------------

src/spectral_utilities.f90

@@ -146,8 +146,6 @@ module spectral_utilities
    FIELD_DAMAGE_ID
  private :: &
    utilities_getFreqDerivative
- external :: &
-   PETScErrorF                                                                                      ! is called in the CHKERRQ macro
 
 contains
 
@@ -209,8 +207,6 @@ subroutine utilities_init()
    scalarSize = 1_C_INTPTR_T, &
    vecSize = 3_C_INTPTR_T, &
    tensorSize = 9_C_INTPTR_T
- external :: &
-   PetscOptionsInsertString
 
  write(6,'(/,a)') ' <<<+-  spectral_utilities init  -+>>>'
  write(6,'(/,a)') ' Eisenlohr et al., International Journal of Plasticity, 46:37–53, 2013'